Apparatuses of the kind referred to above are used to produce multi-layered absorbent cores, at least one of the layers containing discrete particles of a highly absorbent material, preferably a so called superabsorbent material (SAP), which can absorb liquid in an amount several times it own weight. The fibres in the layers are preferably cellulosic and produced by defibration of pulp. Additionally, other types of fibres can be added. The fibres in the different layers can be the same or different.
Apparatuses according to the present disclosure are to be disposed in a manufacturing line for producing absorbent articles, such as disposable diapers, sanitary napkins, incontinence protectors and the like sanitary articles. It is therefore important that such apparatuses do not occupy a lot of space, especially in the length direction of such a production line. Nowadays, the production rate of such a production rate is high, approximately 600 cores per minute, and the present disclosure aims to allow even higher production rates. In such high speeds the centrifugal forces acting on the discrete particles in formed core elements are quite high and there is a problem of preventing these particles from falling out of such core elements. Apart from the cost consequence of losing relative expensive particle material, there is a risk that the lost particles will fall on components or equipment in the production line an adversely influence the functions thereof and also the environment. Lost particles must therefore somehow be taken care of. There is therefore a need to keep such losses of particles as low as possible.
Another problem is to ensure that the core elements formed on the respective mat-forming wheel of an apparatus of the kind described in the introduction are superposed on each other in the desired mutual relationship. If, for example, the leading edges of the superposed core elements are to be aligned with each other, a misalignment will visually be very apparent and will also adversely influence the function of the produced article. For example, if the produced article contains openings or the like in the superposed cores which should coincide or have a determined relationship relative each other in the superposed position of the core elements, a misalignment of those openings will have a detrimental effect on the functioning of the produced article.
A further problem with an apparatus according to the introduction is that there is a risk that the discrete particles air-laid onto a mould will damage the mould or obstruct or clog some of the openings in the mould. Such obstructions or clogging leads to an uneven distribution of air-laid material in the mould and will consequently adversely affect the absorptive properties of the produced article.
In EP-B1-O 958 801 is shown an apparatus, in which a web of tissue is wound on a mat-forming wheel and drawn against the walls of the moulds on the peripheral surface of the wheel. Thereafter, a layer of discrete particles is air-laid in the mould and air-entrained fibres are drawn into this layer of discrete particles to mix with the discrete particles. In FIG. 3 of this document, such an apparatus having two mat-forming wheels is disclosed. The air-laid bodies are delivered from each mat-forming wheel attached to the webs of tissue and the two webs of tissue together with the attached bodies are then superposed on each other. The bodies attached to the webs travel a rather long distance without suction means influencing the bodies thereon and there is a great risk that particles will fall out of the bodies during this travel. Moreover, with such a construction it seems hard to obtain a great accuracy of the relative positions of the bodies attached to the webs when superposed to each other.
In EP-B1-I 082 081 an apparatus according to the preamble of claim 1 is disclosed. In such an apparatus, only fibrous material is air-laid in the moulds on the first mat-forming wheel for forming a body on which a second body composed of a mixture of fibrous material and discrete particles of SAP is transferred from the second mat-forming wheel while the first body is still in its mould. A third layer of fibrous material is then air-laid over the composite of the first two bodies. During the transfer of the second body onto the first body, a part of the second body is always in the free air exposing both its sides thereto. There is thus a great risk that SAP-particles will fall out of these exposed parts of the second body, especially if the concentration thereof is high and the speed of the mat-forming wheels are high. After transfer of the second body onto the first body, the third layer air-laid thereon will prevent the SAP-particles in the second body from falling out. Although the accuracy of the positions of the superposed bodies is improved due to the first body being maintained in its mould during the transfer of the second body thereon, the second body has to move in free air before being superposed onto the first body, a fact that reduces accuracy. Moreover, in the second mat-forming wheel there are no means for preventing discrete particles air-laid in the moulds to obstruct or clog the openings in the bottoms of these moulds.
Sanitary absorbent articles, such as diapers, are often provided in different sizes. When such different sizes of cores for the “same” absorbent article are to be produced on the same apparatus, like the apparatus described in the introduction, the moulds on the mat-forming wheels have to be changed. This is a time-consuming operation, which also involve storage of the different moulds not used for the size in question and which reduce the cost-efficiency of the manufacturing process, especially for small product series.
For such articles it is also advantageous to have core elements with a high amount of SAP-particles (more than 50%) mixed into the fibrous material. A problem with having such an high amount SAP-particles in a core element is that the strength of the core element is reduced. The risk for losses of SAP-particles during forming and transport of such elements is of course increased.
Due to the above mentioned risks for loss of SAP-particles and the risk for formed cores to be damaged during transport and handling due to the reduced strength of core element with high content of SAP-particles, equipment for forming such cores, such as mat-forming wheels, are disposed within a line for the manufacturing of sanitary article so that the transport of core element formed on the wheels between forming and further treatment of the core is very short. Since mat-forming wheels are large components it would be advantageous if these components could be located at a distance from other components in the manufacturing line so that available space can be used as efficient as possible.